The availability of all silicon-based optoelectronic integrated circuit (OEIC) technology promises to revolutionize the optoelectronic industry and significantly impact a wide range of both military and commercial applications. One such area of impact is multi-chip module interconnectivity. Silicon-based OEICs will not only solve resistivity and high-capacitance problems by replacing electron transport with photons, they will also provide new functionality, such as circuit-level image processing. Silicon OEICs will also provide cost inroads to commercial markets as high-volume silicon processes enjoy economies of scale unparalleled by other electronic or optoelectronic materials technologies. Furthermore, silicon-based OEICs are expected to provide new functionality such as circuit-level image processing.
There are four technologies required to make silicon-based OEICs a reality: (1) detectors; (2) waveguides; (3) modulators and (4) emitters. While there has been considerable progress in the first three areas, a lack of an appropriate silicon-based light-emitting device, particularly a silicon-based laser, has greatly hindered the development of fully integrated silicon-based OEICs technology.
Most work to date on OEICs has been based on III-V materials. However, post-ultra large-scale integrated (ULSI) work will likely continue to use silicon substrates because of low material costs, high mechanical strength, good thermal conductivity, and the highly developed processing methods available for silicon. One approach to integrating optical and digital electronics is to integrate III-V silicon materials using epitaxially grown III-V layers for selected regions on silicon substrates. Although laser action from III-V layers grown epitaxially on silicon has been demonstrated, progress in this area has been limited by material quality problems resulting from the large lattice and thermal expansion mismatch between the two systems and incompatibilities between III-V and silicon processing.
Reduced cavity size has been found to significantly affect laser characteristics for silicon-based lasers. When the cavity length is comparable to the wavelength of the cavity-defined radiation, cancellation of spontaneous emissions, zero-threshold lasing and enhanced gain may be achieved. The degree of gain enhancement is determined by the coherent length of the spontaneously emitted radiation. Gain enhancement has been predicted to increase more than five-fold in III-V semiconductor microcavities as the emission linewidth decreases from 100 nm to 30 nm.
Although possible applications of these phenomena have been considered mostly for semiconductor lasers, the microcavity effects can also be applied to solid state lasers. Solid state lasers generally provide better thermal stability and narrower emission linewidths than semiconductor lasers. The narrow emission linewidths gain media from solid state lasers are ideal for inducing microcavity gain enhancement effects.
A need also exists for a way, to achieve light emission from these films by electroluminscence rather than by photoluminescence. If this were possible, electrons could be used to produce photons and, thus, utilize the optoelectronic devices made of these films through voltage variation.